The present invention relates to a glow plug, and more specifically a glow plug that is highly resistant to shocks and vibrations even when it is longer than conventional. The present invention further relates to a glow plug suitable for a direct injection diesel engine.
For pollution control, a direct injection diesel engine has recently come into use. In some cases, the direct injection diesel engine requires a glow plug longer than conventional.
The glow plug is inevitably subjected to shocks and vibrations transmitted thereto from the engine over a long period of usage, and at the same time, is caused to resonate by the shocks and vibrations. Accordingly, in such a longer glow plug, it is highly likely that a ceramic member is cracked and/or an electric conductor that connects a ceramic heater with an inner pole is broken under the influence of the shocks, vibrations and resonance.
It is therefore an object of the present invention to provide a glow plug that attains excellent durability over a longer period of usage, when it has a length similar to a conventional glow plug.
It is also an object of the present invention to provide a glow plug that is highly resistant to shocks and vibrations, even when it has a greater length than a conventional glow plug.
According to one aspect of the invention, there is provided a glow plug comprising: an outer shell; an inner pole disposed partly in the outer shell and fixed thereto at a plurality of pole fixed portions, the inner pole having first and second ends, the pole fixed portions including first and second pole fixed portions located nearest to the first and second ends of the inner pole, respectively, each of the first and second pole fixed portions having first and second ends located nearer to the first and second ends of the inner pole, respectively; a ceramic heating rod disposed partly in the outer shell in line with the inner pole, the ceramic heating rod having first and second ends, the second end of the ceramic heating rod being located adjacent to the first end of the inner pole; and an electric conductor electrically connecting the inner pole with the ceramic heating rod, wherein a ratio of L2/L1 is larger than 2, where L1 is a distance from the first end of the inner pole to first end of the first pole fixed portion and L2 is a distance from the first end of the inner pole to the first end of the second pole fixed portion.
According to another aspect of the invention, there is provided a glow plug comprising: an outer shell; an inner pole disposed partly in the outer shell and fixed thereto at one or more pole fixed portions, the inner pole having first and second ends, the one or more pole fixed portions including a first pole fixed portion located nearest to the first end of the inner pole, the first pole fixed portion having first and second ends located nearer to the first and second ends of the inner pole, respectively; a ceramic heating rod partly disposed in the outer shell in line with the inner pole and fixed thereto at one or more heating rod fixed portions, the ceramic heating rod having first end and second ends, the second end of the ceramic heating rod being located adjacent to the first end of the inner pole, the one or more heating rod fixed portions including a first heating rod fixed portion located nearest to the second end of the ceramic heating rod, the first heating rod fixed portion having first and second ends located nearer to the first and second ends of the ceramic heating rod, respectively; and an electric conductor electrically connecting the inner pole with the ceramic heating rod, wherein a ratio of L3/L4 is smaller than 15, where L3 is a distance from a middle point between the first end of the inner pole and the second end of the ceramic heating rod to the first end of the first pole fixed portion and L4 is a distance from the middle point to the second end of the first heating rod fixed portion.